Linear alkylbenzenes (LAB) are compounds that have significant commercial importance. Linear alkylbenzene sulfonate (LAS) compounds made by sulfonation of linear alkylbenzene are used in the manufacture of detergents and other products. Because linear alkylbenzenes are more easily biodegradable than branched alkylbenzenes, linear alkylbenzenes have essentially replaced branched alkylbenzenes in detergents and other products. In particular, linear alkylbenzenes with long alkyl chains, such as chains having about 10 to about 14 carbons, are commonly used. However, linear alkylbenzenes with longer chains and with shorter chains also are commercially important.
Linear alkylbenzenes often are made by alkylation of benzene with olefins. Positional isomers, such as 2-phenyl, 3-phenyl, 4-phenyl, 5-phenyl, and the like, result from this alkylation of benzene with long chain olefins. The distribution of the phenyl along the alkyl chain produces different products.
Historically, linear alkylbenzenes are manufactured commercially using classic
Friedel-Crafts condensation employing catalysts such as aluminum chloride, or by using strong acid catalysts such as hydrogen fluoride, for example, to alkylate benzene with olefins. In 1995, a solid bed alkylation process, the Detal™ process, using a solid non-corrosive acid catalyst was introduced. While such methods produce high conversions, the selectivity to the 2-phenyl isomer typically is about 30 percent or less. Linear alkylbenzenes with a high percentage of the 2-phenyl isomer are highly desired because such compounds when sulfonated have long tails that provide enhanced solubility and detergent properties.
The 2-phenyl isomer content of the product is process dependent. Solid alkylation catalysts, such as those used in the Detal™ process, produce products with 2-phenyl isomer content between 25 and 30 percent. HF-catalyzed processes typically yield a 2-phenyl isomer content less than 20 percent, and AlCl3 typically between 30 and 33 percent. The properties of linear alkylbenzenes and linear alkylbenzene sulfonate produced from these three processes have been disclosed by Berna and coworkers in the following publications. Journal of Surfactants and Detergents, Vol. 3, No. 2 (July 2000) pages 353 through 359, JAOCS, Vol. 72, No. 1 (1995) pages 115 through 122, and Tenside Surfactants Detergents 25 (1988) 4, pages 216 through 221.
Zeolite catalysts also have been used to obtain linear alkylbenzenes by alkylation of benzene with olefins. The 2-phenyl isomer content of linear alkylbenzenes obtained using such catalysts depends on the zeolite selected and can vary from about 20 percent to 90 percent. However, some zeolitic catalysts are quickly deactivated, and very high concentration of 2-phenyl isomer in linear alkylbenzene yields a linear alkylbenzene sulfonate that dissolves poorly in water. Most zeolites, with the exception of FAU, produce linear alkylbenzene with 2-phenyl isomer content higher than existing commercial processes.
The differences in linear alkylbenzene compositions produce different linear alkylbenzene sulfonate products. The products differ not only in composition but also in properties and characteristics. Some of the properties that detergent formulators need to consider are solubility, viscosity, detergency performance, foaming power, foam stability, hard water stability, and biodegradability. A number of these properties are dependent on the isomeric composition of the linear alkylbenzene sulfonate.
Thus, there exists a need for a method for controlling 2-phenyl isomer content of linear alkylbenzenes obtained by alkylating benzene with olefins.